bind & connect

[Harald Welte]

On Thu, Oct 13, 2016 at 11:39:17PM +0200, Neels Hofmeyr wrote:
> But how would I tell the IuPS to use a given local interface 1.2.3.5 to contact
> the SGSN's address? 

Please note that on Linux, addresses are always addresses of the overall
host / IP stack and not of a specific interface.  The routing table
is used to determine the local address that should be used for a given
destination.

So for (almost?) all reasonably configured systems, it should simply
work based on what the system administrator has set.

> Would I bind() to a given local IP address and connect() to the remote
> one?

yes.

> AFAIK it can be important to set a local IP address and port to send
> from. 

I think in general this would mostly be a work-around for broken setups.

At least, when talking about TCP clients here.  Binding UDP or TCP
server sockets is of course a different story

> Anyway, in osmo_sock_init, I see:
> 
>         if ((flags & (OSMO_SOCK_F_BIND | OSMO_SOCK_F_CONNECT)) ==
>                      (OSMO_SOCK_F_BIND | OSMO_SOCK_F_CONNECT)) {
>                 fprintf(stderr, "invalid: both bind and connect flags set:"
>                         " %s:%u\n", host, port);
>                 return -EINVAL;
>         }

well, because we only pass one pair of host+port parameters into
osmo_sock_init(), you cannot bind and connect to that same host:port,
unless you insist to only talk to yourself.



> Should we have another osmo_sock_init that can set up a socket like this code I
> found somewhere at sysmocom to define both ends of a connection?

I'm not sure if it should be a new function for both connect + bind at
the same time, or we simply bind using osmo_sock_init() and then have
another call for the connect?

In any case, this is one of the things I wouldn't bother unless
somebody really indicates he needs it.

-- 
- Harald Welte <laforge at gnumonks.org>           http://laforge.gnumonks.org/
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